The present invention relates to utilizing, for the production of straight-chain paraffins, a thermal-cracked oil distillate from a thermal cracking process using a petrolic heavy residual oil.
Recently, because of the exhaustion of petroleum resources, heavier crude oils have come to be used, thus giving rise to an increasing tendency of the amount of heavy oils by-produced such as residual oils in distillations. These heavy residual oils are of less industrial value by reason of their high viscosities or high sulfur and metal contents.
On the other hand, such heavy residual oils can be utilized in thermal cracking processes typified by coking, which may be the only utilization mode of those oils. From the heavy residual coking process is obtained a liquid substance, i.e., thermal-cracked oil, as well as coke and gas. Usually, the yield of the thermal-cracked oil in coking is fairly high and so there are obtained large amounts of thermal-cracked oil distillates.
Since the thermal-cracked oil thus produced in a large amount contains a relatively large amount of aliphatic hydrocarbons and does not have a sufficiently high octane number, such oil has heretofore not been used directly for automobile gasoline, for which purpose it is required to be subjected to a further treatment such as a fluid catalytic cracking. At most, it has been used merely as fuel for boilers, etc. Therefore, how to utilize such large amount of thermal-cracked oil is becoming an important subject in the industrial world.
On the other hand, liquid straight-chain paraffins are starting materials of straight-chain alkylbenzenes and long chain alcohols as surfactant producing materials which are in extremely great demand, and are also starting materials of petroleum proteins. Industrially, liquid straight-chain paraffins have heretofore been obtained mainly by their separation from a kerosene distillate which contains large amounts of straight-chain paraffins according to a molecular sieve process or a urea adduct process. However, such straight-chain paraffins-containing kerosene distillate is becoming difficult to obtain with the recent decrease of paraffin-base crude oils accessability of heavier crude oils.